MRI is an imaging method which excites nuclear spin of an object set in a static magnetic field with a RF (radio frequency) signal having the Larmor frequency magnetically and reconstructs an image based on NMR (nuclear magnetic resonance) signals generated due to the excitation.
Conventionally, a stretcher has been used as an instrument with which the object is placed on a top plate of a bed in the MRI apparatus. The stretcher is constituted of a top plate with which the object is set and a frame with which the top plate is moved. Then, the top plate of the stretcher is overlapped with the top place of the bed utilizing the frame as the object is placed on the top plate of the stretcher.
Specifically, both sides of the top plate of the stretcher are supported by two arms of the frame at two positions separated by longer distance than the longitudinal width of the top plate of the bed. And one of the two arms, which corresponds to the head side of the object, is arranged in a space between the bed of the MRI apparatus and a gantry. On the other hand, the other of the two arms is arranged on the foot side of the bed. Whereby, the top plate of the stretcher on which the object is placed is arranged separately above the bed.
Next, the position of the top plate of the bed is adjusted by an up-and-down adjuster of the bed such that the height position of the top plate of the bed may be higher than that of the two arms of the frame. Whereby, the top plate of the stretcher is supported by the top plate of the bed such that the frame positioned separately from the top plate of the stretcher is retreated. Then, the top plate on the bed is moved in a state that the top plate of the stretcher is overlapped with the top plate of the bed such that the top plate of the bed, the top plate of the stretcher and the object as a whole are moved into the inside of the gantry.
Recently, the number of RF coils for receiving NMR signals tends to increase with respect to the MRI apparatus. Therefore, a bed having connectors of RF coils on the top plate has become more often employed. It is important to make the thickness of the top plate thinner in order to secure an imaging space and an accommodation space for cables of the connectors with respect to a bed having the connectors. Whereas, it is necessary for the top plate of the bed to have rigidity so as to support the weights of the connectors. As a result, the rigidity of the top plate having the connectors is supposed to be enough rigidity to support the connectors.
When such a top plate having the connectors is employed, it is difficult to arrange the bed at a position separate from the gantry in order to secure enough rigidity of the top plate to support the connectors. That is, it may be more likely to cause an impact of movement as the top plate is moved horizontally if the distance between the bed and the gantry becomes larger.
On the other hand, it is preferable to configure the apparatus such that imaging can be performed in condition where less vibration is caused by shortening the distance between the bed and the gantry even in the case that the bed having the top plate of high rigidity without any connectors. Also, lengthening the distance between the existing gantry and the bed having been installed is subject to restriction of arrangement conditions and remodeling costs.
In addition, it is also possible to downsize the apparatus if the length of the top plate can be shortened, while the rigidity of the top plate is improved.
It is an object of the present invention to provide a top plate having a more appropriate structure for a magnetic resonance imaging apparatus, a frame for a top plate set of a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus.